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Makes the 24-70 f4 really worth it huh...not. Great price.
Yes, that 24-70mm f/4 is an odd beast, especially placed against the 24-70 f/2.8 and the 24-105 f/4 IS.
A 24-105mm f/4 L IS at the price mentioned in this thread is a really good value. I've used that lens since a very short time after it was released and it has been an excellent performer for me. No lens is perfect, but this one is very good and the most flexible Canon option in more or less this range.
Among the three current Canon 24-[something else] L zooms, we have an interesting set of features, each with its pluses and minuses. I wrote something about this at my blog - in case you want to read a bit more about it: 24-70mm f/2.8 L II vs. 24-70mm f/4L IS vs. 24-105mm f/4 L IS. Some pluses/minuses of each include:
24-70mm f/2.8 L II - This lens is optically excellent, of course, and provides the largest maximum aperture at f/2.8. Its focal length range is not that large and there are those who feel constrained by the 70mm long end, which falls short of "portrait" focal length. It is the largest and heaviest of the group and lacks IS, and it uses the (somewhat) unusual 82mm filter thread diameter. It is very costly.
24-105mm f/4 L IS - The lens provides very good image quality, though with some issues that buyers would want to know about. The 105mm maximum focal length provides more utility than the 70mm maximum alternatives. Image stabilization let's one shoot in lower light when camera stability is the issue. The lens produces noticeable vignetting at largest apertures, especially at 24mm, and barrel distortion at the shortest focal lengths - though these things are easily correctible in post. Cost is lower and it is often part of kits.
24-70mm f/4 L IS - The lens provides very good image quality. While it might seem like a handicapped 24-105 when considered from some perspectives, it does provide a useful close focusing capability and is the smallest and lightest of the bunch, and it provides a less expensive alternative for covering the 24-70mm range at a lower cost, though many will think that it does not compete with the 24-105 as well as it might on the basis of cost alone.
The good news is that all three of these are quite good lenses, and you could choose any one of them that seems the most appropriate and it can produce excellent quality photographs.